The Herschels were among the most important astronomers of the 18th and 19th centuries. William Herschel (1738 - 1822) is most famous for discovering Uranus in 1781 – the first planet discovered since the ancient Greeks (Herschel 1783). His sister, Caroline (1750 - 1848), apart from assisting William in all of his work, published her own discoveries of comets (Herschel 1787) and is recognized as the first professional female astronomer (Hoskin 2014, 10)1. However, it was their work on nebula – misty, indistinct wisps that we now know are galaxies, star clusters, and clouds of gas – that was most impressive. Not long after Messier published his highly regarded catalog of barely 100 of these objects (Messier 1781), the Herschels had described over 2500 of them (Herschel 1786, 1789, 1802). This work, and what was to come, lead the German astronomer Freidrich Struve to remark,
L’etude de ciel nebuleux parait etre le domaine presque exclusif des Herschel [The study of the nebulae seems to be the almost exclusive domain of the Herschels]
(Struve 1847, 48; Hoskin 2008, 16)
John Herschel (1792 - 1871) continued the family tradition and published his own catalog (2500 nebulae, of which 500 were new) (Herschel 1833). This, he considered, was close to a complete sample of the nebulae visible from northern Europe with current telescopes (20 foot focal length, 18 inch diameter).
is shows pretty evidently our knowledge of the nebulous contents of the northern hemisphere to be at length nearly complete, and that to make a further step, the powers of an instrument like the 40-feet reflector will be required.
(Herschel 1833, 3)
However, there was another way to “make a further step” and discover more nebulae; travel to the Southern Hemisphere and observe new areas of the sky. In November 1833, John Herschel began the two month journey on an East India Company ship to Cape Town2. From the slopes of Table Mountain he spent the next four years sweeping the skies. The result of his work was a catalog of 1708 nebulae, of which roughly 1300 were new, published in 1847 (Herschel 1847). Throughout this work, his attention to detail is apparent and can be easily demonstrated as he, like Galileo, believed in using drawings to record his observations.
It has generally been my practice to make some kind of sketch or drawing, sometimes more, sometimes less elaborate, of any nebula at all remarkable which presented itself.
(Herschel 1833, 3)
One of his most impressive pieces of work is his description of the Orion Nebula. Herschel spent 13 nights between December 1834 and November 1837 observing the positions and brightnesses of 150 stars in the nebula. He used these as landmarks with which to map the gas of the nebula. Herschel spends 7 pages (Herschel 1847, 25 - 32) describing the lengths he went to correctly illustrate this complicated object. We can skip those details here (though they are a wonderful example of scientific honesty – carefully describing what he does and doesn’t know) and just show the results. Below is Herschel’s drawing, done by one man on a mountain more than 250 years ago, compared to an image from the Hubble Space Telescope.3
Note that I have inverted the colors of Herschel’s drawing (the original was dark ink on white paper) and scaled and rotated the Hubble image.
Herschel, Caroline. 1787. “An Account of a New Comet. In a Letter from Miss Caroline Herschel to Charles Blagden, M. D. Sec. R. S.” Philosophical Transactions of the Royal Society of London Series I 77 (January): 1–3.
Herschel, John Frederick William. 1833. “Observations of Nebulae and Clusters of Stars, Made at Slough, with a Twenty-Feet Reflector, Between the Years 1825 and 1833.” Philosophical Transactions of the Royal Society of London Series I 123 (January): 359–505.
Herschel, Mr. 1782. “A Paper to Obviate Some Doubts Concerning the Great Magnisying Powers Used. By Mr. Herschel, F. R. S.” Philosophical Transactions of the Royal Society of London Series I 72 (January): 173–78.
Herschel, Sir, John Frederick William. 1847. Results of Astronomical Observations Made During the Years 1834, 5, 6, 7, 8, at the Cape of Good Hope; Being the Completion of a Telescopic Survey of the Whole Surface of the Visible Heavens, Commenced in 1825.
Herschel, William. 1783. “A Letter from William Herschel, Esq. F. R. S.” Philosophical Transactions of the Royal Society of London Series I 73 (January): 1–3.
———. 1784. “On the Remarkable Appearances at the Polar Regions of the Planet Mars, the Inclination of Its Axis, the Position of Its Poles, and Its Spheroidical Figure; with a Few Hints Relating to Its Real Diameter and Atmosphere. By William Herschel, Esq. F. R. S.” Philosophical Transactions of the Royal Society of London Series I 74 (January): 233–73.
———. 1786. “Catalogue of One Thousand New Nebulae and Clusters of Stars. By William Herschel, Ll.d. F. R. S.” Philosophical Transactions of the Royal Society of London Series I 76 (January): 457–99.
———. 1789. “Catalogue of a Second Thousand of New Nebulae and Clusters of Stars; with a Few Introductory Remarks on the Construction of the Heavens. By William Herschel, L L. D. F. R. S.” Philosophical Transactions of the Royal Society of London Series I 79 (January): 212–55.
———. 1791. “On Nebulous Stars, Properly so Called. By William Herschel, Ll.d. F. R. S.” Philosophical Transactions of the Royal Society of London Series I 81 (January): 71–88.
———. 1795. “Description of a Forty-Feet Reflecting Telescope. By William Herschel, Ll. D. F. R. S.” Philosophical Transactions of the Royal Society of London Series I 85 (January): 347–409.
———. 1802. “Catalogue of 500 New Nebulae, Nebulous Stars, Planetary Nebulae, and Clusters of Stars; with Remarks on the Construction of the Heavens.” Philosophical Transactions of the Royal Society of London Series I 92 (January): 477–528.
Hoskin, Michael. 2008. “Nebulae, Star Clusters and the Milky Way: From Galileo to William Herschel.” Journal for the History of Astronomy 39 (August): 363–96. https://doi.org/10.1177/002182860803900306.
———. 2014. “Caroline Herschel’s Life of ‘Mortifications and Disappointments’.” Journal for the History of Astronomy 45 (4): 442–66. https://doi.org/10.1177/0021828614537940.
Messier, Charles. 1781. “Catalogue Des Nébuleuses et Des Amas d’Étoiles (Catalog of Nebulae and Star Clusters).” Connoissance des Temps ou des Mouvements Célestes.
Struve, Friedrich Georg Wilhelm. 1847. Etudes d’Astronomie Stellaire: Sur La Voie Lactee et Sur La Distance Des Etoiles Fixes.
I’m hugely underselling William and Caroline as we would never get to the point if I listed all that they did. A short list: They started life as musicians, began astronomy as a hobby, designed and built the best telescopes for their time (Herschel (1782), Herschel (1795)), identified the first planetary nebula (Herschel 1791), discovered the Martian ice caps (Herschel 1784), discovered many moons of the outer planets… I could go on.↩︎
His ship was the last to leave for Cape Town that year “An awful hurricane … followed by a series of south-west gales … prevented any vessel sailing for six weeks”↩︎
Hubble Space Telescope, NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team, available here↩︎